Local filtering operations on two qubits
Frank Verstraete, Jeroen Dehaene, and Bart DeMoor
Phys. Rev. A 64, 010101(R) (2001) - Published 5 June, 2001
Four-photon entanglement from down-conversion
Harald Weinfurter and Marek Żukowski
Phys. Rev. A 64, 010102(R) (2001) - Published 7 June, 2001